TestConsole/ConsoleApp1/InterfaceTest.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp1;

public interface IT1
{
    public void F1(DateTime? dateTime = null);
}
internal class InterfaceTest : IT1
{
    public void F1(DateTime? dateTime = null)
    {
        
    }
}